Digital Voting

Digital voting is a system feature that allows the receive coverage of a repeater to be extended. It also solves problems with dead spots where there isn't sufficient signal from the transmitting radio to reach the repeater.

In a two-way radio system, a repeater or RF site, is typically located at an elevated area such as the top of a hill or tall building; has a higher powered transmitter and high gain antenna. This means that all the radios operating within the desired service area can receive signals at an acceptable strength. However, portable radios have considerably lower ERP because of size and power considerations. The result is that while all the radios within the service area of the RF Site can receive good signals, the RF site may not be able to receive transmissions from radios at all or very well. In other words, the outbound (repeater-to-radio) coverage is almost always far better than the inbound (radio-to-repeater) coverage.

To address this imbalance, multiple receive-only repeaters (satellite receivers) can be installed at various locations throughout the service area to pass the radio’s transmission onto the repeater. Once a satellite receiver receives an acceptable signal from a transmitting radio, it will be relayed back to the voting repeater via an IP connection. The voting repeater then repeats (retransmits) the relayed signal at a sufficiently high power level such that all radios in the service area are able to receive it.

However, depending on where the transmitting radio is, the repeater itself (via its internal receiver) and one or more satellite receivers might also receive the same transmission at an acceptable signal strength. In this case, the repeater examines all of the incoming signals; selects the clearest signal and ignores the rest. This selection is accomplished by means of a voting process. Typically, the voting process analyzes each received signal and determines which one is the best based on the RSSI and/or BER.

By selecting the clearest signal from all receivers, the effects of local interference or fading are reduced. The net result is improved voice and data quality.

Operation

Single Site

The above diagram (left) shows a single repeater system with seven satellite receivers. The repeater in the center, is configured as the voting repeater. The voting repeater is able to transmit and receive whereas the satellite receivers can only receive.

The satellite receivers pass their received signal to the voting repeater. In order for a transmitted signal to be regarded as valid by the satellite receiver, it must have a matching colour code. RAS validation is carried out by the voting repeater. The satellite receivers will also only pass the received signal to the voting repeater which it is configured to communicate with. If a second channel were to be added, it too would require a voting repeater and any number of satellite receivers.

Depending on the system design, the voting repeater could be a Master or Peer repeater.

In practice (diagram on the right), the radio user (green) is closest to Satellite Repeater 5 and hence the RSSI there is the highest. The signal from all the repeaters is evaluated by the voting repeater, and because Satellite Repeater 5 produces the best incoming signal, it's signal is repeated. Note that the Voting Repeater also checks its own inbound signal and may use that instead of whatever is being received by a satellite receiver.

Capacity Plus

The below diagram shows (high level) a single site Capacity Plus system. The Master and Peer repeaters which make up this Capacity Plus system are located in Site 2. Site 1 and 3 house the satellite Receivers. There is IP connectivity between all three RF Sites.

Repeater 11 and 31 feed their received signals to Repeater 21. These three repeaters receive on the same frequency, however only Repeater 21 can transmit. The incoming signals from all three repeaters is compared for signal strength and bit error rate (BER), Repeater 21 selects the best and transmits this.

Similarly, Repeater 12 and 32 feed their received signals to Repeater 22. These three repeaters receive on the same frequency, however only Repeater 22 can transmit. The incoming signals from all three repeaters is compared for signal strength and bit error rate (BER), Repeater 22 selects the best and transmits this.

During a call, the signal quality is continuously monitored and, if need be, either Repeater 21 or 22 will make the switch.

Assuming Radio C wishes to make a call. The call setup will take place on the Rest Channel. The Rest Channel could be present on either Repeater 21 or 22 but for the purposes of this illustration it is on Repeater 21, timeslot 2. The call request from Radio C is received by Repeater 31; 21 and 11. The received signals are passed to Repeater 21 where they are compared. In this case, the signal received by Repeater 11 is very weak; the signal from Repeater 21 is marginal and the signal from Repeater 31 is good. The signal from Repeater 31 is therefore chosen. This signal is also retransmitted by Repeater 21 and received by all the radios on the Rest Channel (A and B) and the Rest Channel now becomes a Voice Channel. All radios which are party to this call will remain and participate in the call while others will move to the new Rest Channel - on the next free timeslot.

Assuming Radio A and B are party to the call requested by Radio C. Both of these radios will remain on what was the Rest Channel. The user of Radio C make a voice call and the user of Radio B responds. The signal from radio B is received with better signal quality at Site 2 - Repeater 21. This signal is selected and retransmitted by Repeater 21. Remember that Repeater 21 and 22 will also use their own received signal to vote.

At the end of the call, all radios that were party to this call will move to the new rest channel as is normal in a Capacity Plus system.

Components

Systems Supported

Digital voting is available in all system configurations except Capacity Max and ERDM. This is also a digital-only feature.

Satellite Receiver

A Satellite Receiver is used in conjunction with digital voting is enabled in the system. The satellite receiver is a receive-only repeater configured to pass the received signal to the Voting Repeater via an IP link.

Voting Repeater

The voting repeater “votes” on all the transmissions received from the satellite receivers, together with whatever signal it received itself. The voted signal is usually the strongest and/or has the lowest BER - it is also retransmitted. There would typically be one voting repeater and several satellite receivers - all would have the same receive frequency.

Supported Hardware and Firmware

R02.30.00 firmware is needed to support digital voting.

• MTR3000 and 32MB DR3000 series repeaters
• SLR1000; SLR5000 and SLR8000 series repeaters
• MTR3000 Receiver only models.

RDAC

RDAC can be used to control digital voting such as enabling or disabling the feature, force vote, and display voting status. When viewing RDAC in a system with digital voting, the following status messages may be displayed:

• Repeater Voting Enabled/Disabled. This status displays whether the voting feature on a repeater is enabled or disabled.
• Force Vote. This status indicates when the receiver is force voted.

There are situations when a particular satellite receiver or the repeater needs to be always selected as the voted winner for a period of time. For example, a critical activity near a particular receiver occurs, thus calls from that receiver need to have higher priority. This can be achieved through force vote from RDAC. When the RDAC user force-votes a particular satellite receiver/repeater, the transmissions received from that particular receiver/repeater is always selected as the voted winner, and repeated until force vote is canceled, or until the force-voted receiver is disconnected from the system.

Note that when voting is disabled on the Voting Repeater, RDAC will not display any voting status for the connected satellite receivers. When voting is enabled on the Voting Repeater, RDAC then displays each satellite receiver’s voting status. The Voting Repeater pushes this information to RDAC and the update frequency is defined by the Voting Status Update Rate configured in RDAC.

Additionally, Satellite Receivers may also display one of the following status messages:

• N/A. This is the default value. Before RDAC obtains any information, this value is displayed.
• Disabled. The receiver is voting disabled.
• Not Synced. The receiver is voting enabled but has not synchronized with the repeater. The satellite does not operate in this state. This could happen during power up, or in a congested IP connection between the receiver and the repeater.
• Synced. The receiver is voting enabled. It has synchronized with the repeater, but not receiving valid over the air transmission.
• Receiving. The receiver is voting enabled, and is currently receiving valid transmission, but is not the voted winner. While in this condition, RDAC also displays the signal quality estimation (SQE). The SQE result is based on the voting parameters, and is categorized as “Excellent”, “Good”, “Fair”, “Poor”, and “Bad/Rejected”.
• Voted. The receiver is voting enabled, currently receiving valid transmission, and is the voted winner. While in this condition, RDAC also displays the SQE based on the available voting parameters.

The voting repeater has a built-in receiver, and is defined as the “internal receiver”. When voting is disabled, RDAC does not display its internal receiver’s voting status. When voting is enabled, RDAC displays its internal receiver's voting status. The repeater pushes this information to the RDAC, and the update frequency is defined by the “Voting Status Update Rate” setting in RDAC. In this case, the following voting statuses are possible:

• N/A. This is the default value. Before RDAC obtains any information, this value is displayed.
• Not receiving. The receiver is not receiving any valid OTA transmission.
• Receiving. It is currently receiving valid transmission, but is not the voted winner. While in this condition, RDAC also displays the SQE based on the available voting parameters.
• Voted. It is currently receiving valid transmission, and is the voted winner. While in this condition, RDAC also displays the SQE based on the available voting parameters.

The satellite receiver reuses repeater hardware like the alarms and failure reports. All existing repeater alarms/failure reports, except for transmit only ones, are still available for the satellite receivers. Remember that the satellite receivers do not transmit so there would be no PA failure message.

Design Considerations

General

Up to eight Satellite Receivers can be used per Voting Repeater in a Conventional Single Site system. The same is true for IPSC Repeaters with both timeslots set up as Local Area Channels.

If RDAC, MNIS or other Link Establishment applications (e.g. dispatcher that doesn't use NAI Voice) are present in the system, the following rule applies:

• For every four RDACs or data applications, the maximum number of satellite receivers are reduced by one
• For every two voice applications, the maximum number of satellite receivers are reduced by one.

In an IPSC system, each site can have anything up to eight satellite receivers. It is not necessary for the number of satellite receivers to be the same at each site. It is also not necessary to have satellite receivers at all sites.

The maximum number of satellite receivers for a specific voting repeater at a site depends on the number of repeater sites as well as the number of RDAC and MNIS instances. The below table shows the maximum number of satellite receivers supported per voting repeater per site in a multi-site system such as MSCP and IPSC.

Maximum Number of Satellite Receivers Per Voting Repeater Per Site as a function of the Number of RF Sites

Number of RF Sites	Max. No. of Satellite Receivers Per Voting Repeater Per Site
1	7
2	6
3	5
4	5
5	5
6	4
7	4
8	4
9	3
10	3
11	3
12	3
13	2
14	1
≥15	0

Capacity Plus

In EMEA, the satellite receivers in a Capacity Plus (Single/Multisite) system do not require either Capacity Plus CfS licence. Only the voting repeater requires a Capacity Plus or Multisite Capacity Plus CfS licence.

In a single site Capacity Plus system, the maximum number of satellite receivers supported for a RF channel is eight.

Remember that, even with Capacity Plus, for every four RDAC or data applications included in the system, the maximum number of satellite receivers needs to be reduced by one. For every voice application included in the system (e.g. voice console) the maximum number need to be reduced by two.

In order to obtain the same Trunked Channel inbound/outbound coverage from channel to channel, each Trunked RF Channel must have the same number of satellite receivers. These receivers must also be at the same location as the receivers for the other system channels.

It is recommended to place a satellite receiver for each Data Revert RF Channel to achieve the same inbound/outbound coverage as the voice channels. However, this is not a requirement.

The same is true for Multisite Capacity Plus: in order to obtain the same Trunked Channel inbound/outbound coverage from channel to channel, each Trunked RF Channel requires a satellite receiver at any selected satellite receiver location. Hence, each Trunked RF Channel requires the same number of satellite receivers altogether. It is recommended to place a satellite receiver for each Data Revert RF Channel to achieve the same inbound/outbound coverage as the voice channels.

It is not necessary for the number of satellite receivers to be the same at different RF sites in a Multisite Capacity Plus system.

IP Networking

The satellite the receiver site must not be in the same LAN as the voting repeater site.

In order for voting to function correctly, the one way network delay between the voting repeater and any of its satellite receivers must be less than or equal to 40 milliseconds. Additionally, the network asymmetry between the voting repeater and the receivers must be less than or equal to 12 milliseconds. The network asymmetry is the absolute value of the time difference for an IP packet to travel from the repeater to the receiver, and from the receiver to the repeater.

Enhanced GPS

If digital voting is enabled in a system with Enhanced GPS, some of the window sizes cannot be used:

• For Capacity Plus Single Site, all window sizes 1 to 2 with CSBK data feature enabled, or 5 to 10 may be used. Examples of such systems are Conventional Single Site.
• If the system is a single site IP Site Connect system, all window sizes 1 to 2 with CSBK data feature enabled, or 5 to 10 may be used.
• For multisite IPSC or Capacity Plus Multi Site, if the IP delay between sites is up to 60 milliseconds, the window size must be 1 or 2 with CSBK data feature enabled, otherwise greater than 7. If the IP delay is up to 90 milliseconds, the window size must be 1 or 2 with CSBK data feature enabled otherwise greater than 8.

If not set correctly, GNSS data may not be transmitted or received properly on system with enhanced GPS and voting.

DV Stability Factor

This parameter is configured using CPS/RM. Voting is partially dependent on the quartz oscillator in the satellite receivers. The accuracy of this oscillator is dependent on a number of factors such as receiver age and temperature. To ensure optimum performance, 0.5 (default) should always be used. However, if constant timeslot swap due to extreme non-network environmental conditions is observed between the receiver and its voting repeater, the value can be increased to solve this specific problem.

Configuration

A system with digital voting is configured the same way as it would have been without this feature. However, the following additional settings need to be adjusted in each voting repeater.

1. Operation Mode needs to be set to Normal Repeater.
2. The Radio ID (not shown) must be unique.Similarly, the following settings are needed in each satellite receiver.

1. Operation Mode needs to be set to Digital Satellite Receiver.
2. Digital Voter Peer ID must be set to the Radio ID of the Voting Repeater which this receiver will send its signal to.
3. The RX frequency is the same as the Voting Repeater.

See Also

IP Site Connect

Capacity Plus